BTO: Where do house martins go in winter?

A house martin collects mud for its nest. Picture by John Harding/BTO ANL-140926-114246001
A house martin collects mud for its nest. Picture by John Harding/BTO ANL-140926-114246001
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Although there are still house martins around, most of these familiar birds will now have left the county, heading south to distant wintering grounds.

The sense that they might have left a little early this year is supported by records from BirdTrack ( which suggest that house martins departed a fortnight or more earlier this autumn than is usual.

Perhaps rather surprisingly, we know very little about where in Africa our breeding house martins spend the winter. There is just a single record of a British house martin from south of the Sahara, a young bird ringed in September 1983 and trapped in Nigeria just five months later. It is thought that our house martins winter over the equatorial jungles of West and Central Africa but we don’t know this for certain. Plans to follow departing house martins with tiny tracking devices may well be realised within the next few years, the devices now becoming small enough for deployment on these long-distance migrants.

Our house martin populations are thought to have undergone a substantial and rather rapid decline during the 1980s, from which the population has not recovered. It is, however, difficult to keep tabs on this species because of its loosely colonial nesting habits and strong association with human settlements. This leaves some uncertainty around our understanding of why their populations might be changing. Are they experiencing problems here in Britain or is the decline a consequence of things happening elsewhere along their migration routes or on their wintering grounds?

In an attempt to improve our knowledge of what is happening to house martins here, the British Trust for Ornithology (BTO) has been trialling some new methods for surveying house martin colonies over the summer. Volunteers and BTO staff have been visiting colonies at sites across the east of England, including Suffolk, to refine methods that will be rolled out as part of a national survey in 2015. Funding for the 2015 work is being sought through the House Martin Appeal, which has just launched. In addition to the national survey of house martin numbers, additional work will examine what is happening at individual colonies. BTO researchers want to find out whether house martins favour particular types of building or specific features – such as wooden barge boards – when placing their mud pellet nests. They also want to get a handle on the number of nesting attempts that individual birds make and the level of success they enjoy.

It is remarkable that we should know so little about the house martin. Not only is it an engaging little bird but it is also one that nests alongside us. The planned national survey raises the prospect that many of the gaps in our understanding will be filled over the coming years. By the time that our house martins return next spring that work will already be under way.